The application generally relates to charge amplifier circuits. The application relates more specifically to a charge amplifier circuit for high temperature downhole applications, e.g., geothermal and oil and gas exploration.
High temperature microseismic tools may be used for the characterization and development of enhanced geothermal systems (EGS). Accelerometers may be used to measure shock and vibration phenomena over a broad temperature range in geothermal applications. Charge mode accelerometers operate by generating a charge output in response to forces created by input vibration or shock acting upon a seismic system. Because of the high impedance level of the charge mode signal generated by piezoceramic crystals in the accelerometer, a special type of amplifier called a charge amplifier is used to condition the very high impedance electrostatic charge signal. The charge amplifier converts the charge to a low impedance voltage mode signal without modifying the charge signal.
Typically diagnostic tools such accelerometers and charge amplifiers are employed in harsh environments such as drill holes at depths of 3,000 meters or more where temperatures may be extremely high. Microseismic tools may provide real-time data from the downhole environment to improve the drilling process and allow quicker detection of problems for more efficient drilling.
Existing charge amplifiers are comprised of components that can withstand only a limited range of temperatures, e.g., up to about 225° C., which are unsuitable for extended exposure to deep bore hole conditions. Heat shields may be used to enclose the charge amplifiers to increase the application temperatures. However, heat shielded amplifiers cannot remain in a deep bore hole for extended periods of time.
Further, charge amplifiers designed for accelerometer interfaces may be limited to the specific impedance properties of the accelerometer. Such amplifiers are unsuited for use as general instrumentation amplifiers other than accelerometers, requiring the user to design a separate amplifier for general instrumentation.
Intended advantages of the disclosed systems and/or methods satisfy one or more of these needs or provide other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the claims, regardless of whether they accomplish one or more of the aforementioned needs.